1. Field of the Invention
The present invention relates to a device for dispatching pests through electrocution; more particularly the present invention uses a resistive switch, coupled to a conductive plate, to detect the presence of a pest between the plate and ground, and to trigger a high voltage and current which is supplied through the same electrodes used to sense the pest of sufficient amplitude to electrocute the pest.
2. Description of the Related Art
Residential areas, farms and ranches are often disrupted by burrowing pests such as gophers and the like, which can cause large amounts of physical and economic damage to such grounds. Urban areas, industrial plants and large food manufacturing and preparation facilities are often plagued by the presence of rats and mice. Numerous traps have been designed in the past for eliminating such pests by various means including electrocution. Prior art traps, however, suffer from various deficiencies.
Existing devices typically have very complicated structures that are costly to manufacture. Further, these designs are not conveniently employed without disruption of the rodent's natural environment, making it more likely that rodents will seek to avoid them as foreign because of their disruptive nature.
Finally, these prior art traps do not always reliably sense the presence of a rodent or reliably dispatch the rodent which has been sensed. For example, some prior art traps supply a continuous high voltage which not only requires a considerable supply of power, but may not completely dispatch the rodent if good contact is not made between the rodent and the high voltage terminals. In addition, some pests may be able to sense the presence of the high voltage without making sufficient contact for electrocution.
Most prior art designs that employ triggers are mechanically actuated, requiring the pest to exert the force necessary to close contacts; such mechanical switches can be very unreliable. Some prior art designs attempt to trigger the device through a separate sense contact, which permits triggering of the high voltage output without need for some force to be exerted by the pest.
While this design eliminates the unreliability associated with mechanical actuation, it only assures good contact between the rodent and the sense contact, not between the pest and the high voltage electrodes. A pest may be in physical contact only with the sense electrodes. Environmental conditions such as temperature and humidity may not sufficiently decrease conductivity between the pest and the sense contact to impede the sense function, while conductivity between the pest and the high voltage contacts may be sufficiently reduced to prevent the level of current flow from reaching a lethal level. Rodents that encounter such traps without lethal results can learn to avoid them in the future. U.S. Pat. No. 4,048,746 issued on Sep. 20, 1977 to Joseph R. Dye illustrates many of the difficulties of such a prior art trap. The patent shows an electronic device used to exterminate rodents in their burrows without the removal of soil; the design attempts to minimize its impact on the rodent's natural environment. The device includes a stick-type carrier for insertion into the soil, a metal sleeve which is installed on the tip of the carrier constituting an electric ground, and two brass rings which are secured on the stick-type carrier serving as sense control and high voltage electrodes. The device further includes a circuit which is connected to the metal sleeve and the two brass rings to test the location of a burrow and provide high voltage and current. The circuit includes two control transistors, a relay and a high voltage transformer. The circuit is also provided with a light which gives a continuously visual alarm indicating that a rodent has been electrocuted.
This device has many shortcomings for which the present invention provides solutions. First, this device employs two sets of contacts, one to sense the rodent's presence, and a second to provide the lethal dose of high voltage and current. As previously discussed, the fact that sufficient contact has been made between the rodent and the sense contacts does not guarantee that good contact has been made between the rodent and the high voltage contacts. Thus, the design permits the rodent to avoid good contact with the high voltage electrodes, and even to avoid contact with the carrier altogether.
Further, the conductivity of the sense contact will not necessarily be affected by environmental conditions in the same way that the high voltage contacts are. Thus, the sense contacts may be sensitive enough to indicate the presence of the rodent even though the conductivity of the high voltage contacts have been affected to such an extent that they cannot provide a lethal current. The rodent must make good contact between the two contacts on the apparatus for the lethal current to flow.
This device also consumes a good deal of power unnecessarily because the alarm light is illuminated continuously until the user removes the carrier. Finally, even if the rodent makes optimal contact with the carrier, the design permits the shock itself to easily disengage the rodent from the carrier, thus making it imperative that the rodent be electrocuted within a very short period of time subsequent to the onset of the high voltage and current.
U.S. Pat. No. 3,468,054 issued on Aug. 15, 1967 to Irving Levine discloses an electrical rodent exterminator. The exterminator includes a casing which has a rodent entrance chamber and metal grids therein. A bait is disposed on the rear wall in the casing. The front of the rodent entrance chamber is open for rodents. There is a swinging baffle hanging vertically in the chamber. If a rodent which comes into the chamber for the bait stands on the grids and pushes the swinging baffle, the swinging baffle will rotate a rod which, in turn, closes the switch in a circuit for electrocuting the rodent. The circuit includes a transformer and a clock timer for providing a timed cycle of high voltage current to the grids. The circuit also has a signal lamp which is turned on after electrocution. Obviously, this type of exterminator has a complicated structure and is not suitable for use in a burrow or other restricted area due to its large size. The exterminator is also power inefficient due to the continual illumination of the signal lamp. In addition, this device is not efficient because electrocution of the rodent requires that the rodent first find the entrance, then move into the chamber, and finally push the swinging baffle in order to trigger the circuit.
Other conventional rodent traps are disclosed in a number of patents including U.S. Pat. No. 4,780,985 issued on Nov. 1, 1988 to Clande G. Coots; U.S. Pat. No. 4,497,130 issued on Feb. 5, 1985 to John P. Fitzgerald; U.S. Pat. No. 4,205,480 issued on June 3, 1980 to William J. Gartner; U.S. Pat. No. 3,827,176 issued on Aug. 6, 1974 to Homer A. Stirewalt; U.S. Pat. No. 4,074,456 issued on Feb. 21, 1978 to Robert Wayne Tedwell; U.S. Pat. No. 3,792,547 issued on Feb. 19, 1974 to Leon E. Day; U.S. Pat. No. 3,197,916 issued on Aug. 3, 1965 to S. L. Cole, Jr., et al; U.S. Pat. No. 3,388,497 issued on Jun. 18, 1968 to I. Levine; U.S. Pat. No. 909,814 issued on Jan. 12, 1909 to Hosea Haxton; U.S. Pat. No. 1,680,594 issued on Aug. 14, 1928 to T. F. Connolly et al; U.S. Pat. No. 2,003,513 issued on Jun. 4, 1935 to L. D. Myers; U.S. Pat. No. 2,098,884 issued on Nov. 9, 1937 to E. B. Rousseau; U.S. Pat. No. 2,161,789 issued on Jun. 13, 1939 to G. L. Wingfield; U.S. Pat. No. 2,191,127 issued on Feb. 20, 1940 to C. T. Hazel; U.S. Pat. No. 2,420,723 issued on May 20, 1947 to H. L. Ratchford; and U.S. Pat. No. 2,595,130 issued on Apr. 29, 1952 to L. R. Edwards. These conventional rodent traps normally include a chamber or channel in which a bait is used to attract the rodent. The rodent has to find the entrance of the chamber before taking the bait. When a mechanical switch in the chamber is touched or moved by the rodent, a circuit is completed to electrocute the rodent. In some of the conventional rodent traps, two elements have to be contacted or pushed at the same time by the rodent in order to trigger the circuit. In addition, these traps are either complicated to manufacture or are inconvenient to use.!
U.S. Pat. No. 5,269,091, issued on Dec. 14, 1993 to William Johnson, et al., discloses a rodent electrocution device with a design which solves some of the shortcomings of the prior art previously discussed. The disclosed trap has a specially designed mechanical structure the purpose of which is to employ the weight of the pest to trigger the high voltage circuit and to ensure a good contact between the rodent and the high voltage contacts.
While this design provides improved performance over the prior art previously discussed, its enhanced performance is primarily due to innovations that are concentrated in the mechanical portion of the circuit. As a result, this design still presents some problems with respect to cost of manufacture, ease of implementation and reliability. Therefore, there is still room for further advancement in the art of pest elimination through electrocution.